This invention relates generally to microlenses and to photodetectors which may be used, for example, for digital imaging devices including cameras and scanners.
Photodetectors are used to detect light in a digital imaging device. A large number of photodetectors may each detect a light intensity value for a given pixel. These light intensity values are digitized and used to form a digital depiction of a particular image. Such imaging devices are used in digital cameras, scanners and other devices.
The imaging device may be formed, for example, using complementary metal oxide semiconductor (CMOS) technology. Imaging devices made using CMOS technology include active pixel sensors (APS) and passive pixel sensors (PPS). Alternatively, the imaging device may use charge coupled device (CCD) technology. All of these devices can be made of particularly small size.
Imaging arrays of particularly small size may have a fill factor problem. The fill factor is the amount of light that falls on any given photodetector. Ideally, the amount of light that falls on each photodetector is designed to be as high as possible to improve the signal to noise ratio. In order to improve the fill factor with small photodetectors, a microlens may be situated over the photodetector. The microlens focuses all the light incident on a pixel onto the photodetector and therefore improves the fill factor of the photodetector.
However, with conventional microlenses, formation of these relatively small microlenses with high precision and tolerance may be difficult. For example, the devices may require elaborate temperature or etching conditions which make their fabrication time consuming and expensive. In addition, the optical clarity of some microlenses adversely affects the incoming light.
Therefore, it would be desirable to have a microlens with improved characteristics.
In accordance with one embodiment, a photodetector includes diffractive lens elements. A photosensitive device is arranged to receive the light through the lens elements.